The present invention relates to vacuum degassing and pulse-dampening systems generally, and more particularly to vacuum degassing, pulse-dampening systems for use in liquid chromatography applications. This invention also relates to methods for dampening flow pulsations and degassing mobile phase materials.
A variety of applications exist today involving the use of fluid solvents or reactants, wherein the presence of dissolved gases, particularly air, is undesirable. One example of such an application relates to mobile phases in high performance liquid chromatography, where the presence of even small amounts of dissolved gases can interfere with the accuracy and sensitivity of the results obtained. In some cases, the dissolved gases can form bubbles in the mobile phase, thereby causing measurement error in chromatographic applications. Furthermore, some dissolved gases can cause deleterious effects on the mobile phase as well as the surrounding componentry. Often times, such detrimental effects caused by the dissolved gases is related to the relative concentration of the gases in the mobile phase. To avoid such effects, the gases are typically removed from the mobile phase through a known degassing process.
An additional issue that exists in present liquid chromatography systems involves the necessity of dampening fluid pressure pulsations flowing through respective flow conduits and through respective chromatographic columns, which pulsations result from uneven draw and discharge from positive-displacement fluid pumps, such as reciprocating pumps. To obtain the most accurate chromatographic measurements possible, fluid (mobile phase) flow through the column and the detector should be nearly constant. Thus, in order to obtain a continuous fluid flow at a substantially constant rate, it is desirable to provide the chromatographic system with a pulse-dampener in the fluid flow conduit between the fluid pump and the column/detector.
Fluid pressure pulsations in liquid chromatography systems may also occur upstream from respective fluid pumps, thereby adversely affecting chromatographic operations upstream from the fluid pump. In many applications, the mobile phase transported through the liquid chromatography system is a blend of multiple solvents. In such embodiments, individual solvent reservoirs are operably connected to a blending valve apparatus to blend desired quantities of the distinct solvents into a unitary mobile phase. Solvent may be drawn from the respective reservoirs into the blending valve apparatus by a downstream fluid pump, which pump subsequently delivers the blended mobile phase to the remaining chromatographic components. Because of the pulsation characteristics of the fluid pump, it is desirable to provide mechanisms for dampening such pulsations between the respective solvent reservoirs and the blending valve apparatus, as well as downstream from the blending valve apparatus. Fluid flow pulsations drawn into the blending valve apparatus have the tendency to decrease the accuracy of the blended mobile phase, such that desired ratios of respective solvents comprising the blend may not be accurate. Further, fluid flow pulsations into the blending apparatus can negatively effect physical componentry in the blending valve apparatus, and may decrease the overall life expectancy thereof. It is therefore desirable to provide a pulse-dampening characteristic to the fluid flow conduits connecting such chromatographic components, and particularly between respective fluid reservoirs and a mobile phase blending apparatus.
A number of pulse-dampening techniques have been implemented to provide such flow-dampening characteristics in liquid chromatography applications. For example, fluid has been routed into expandable chambers, wherein a sudden influx of fluid pressure causes the expandable chamber to correspondingly expand, thereby increasing internal volume and absorbing excess fluid pressure to maintain a relatively constant fluid pressure downstream of the expandable chamber. Such flow-dampening devices, however, can result in non-laminar flow patterns, which may result in detrimental formation of gas bubbles in the bulk of the mobile phase. As described above, such gas bubbles can interfere with accurate chromatographic analysis.
Other proposed systems provide dead volumes in the fluid flow pathways, which volumes are not completely filled in standard flow regimes. Upon fluid flow pulsations, however, the dead volumes accumulate the excess fluid flow, thereby mitigating the flow impact downstream of the dead volumes. As with the expandable chambers, however, the dead volumes may act to promote non-laminar flow in the fluid conduits.
Some applications utilize elliptical or flattened tubes as pulse-dampening fluid conduits. Such pulse-dampening tubes are sufficiently flexible to change in cross-sectional profile when a fluid pulse is directed through the tubes. Typical such applications, however, surround the flexible tubing with restraining means for limiting the extent of cross-sectional distention. Such restraining means act against change in cross-sectional profile of the fluid conduits so that the fluid conduits return to an elliptical or flattened profile after the fluid pulse has been dampened. Such restraining means include biasing means, external bodies, and compressible fluids surrounding the fluid conduits.
In addition, the flow-dampening systems proposed to date fail to address the degassing issue in liquid chromatography applications as described above. A particular method of degassing mobile phases includes the use of semi-permeable synthetic polymer resin materials as a fluid conduit material, and the exposure of such a semi-permeable conduit to a reduced pressure or vacuum environment. To perform the degassing, the fluid to be degassed is caused to flow through the conduit in the reduced pressure environment, which allows the dissolved gases to escape from the mobile phase through the semi-permeable conduit walls. By addressing both the degassing functions and the flow-dampening functions in a single apparatus, increased chromatographic efficiency and reduced-sized chromatographic instruments may be achieved.
Accordingly, it is a principle object of the present invention to provide a means for simultaneously degassing a mobile phase and dampening pulsations in such a mobile phase using one or more semi-permeable tubes.
A further object of the present invention is to provide a fluid pulse-dampening apparatus having degassing capabilities.
A still further object of the present invention is to provide a substantially elliptical-shaped flexible tube for dampening flow pulsations and for degassing fluids passing therethrough.
A yet further object of the present invention is to provide a substantially elliptical-shaped flexible tube in a reduced-pressure chamber for degassing fluids passing through the tube, which tube further acts to dampen fluid pulsations passing therethrough.
Another object of the present invention is to provide a flow-dampening degassing apparatus capable of withstanding fluid pulsations of up to about 100 pounds per square inch.
A still further object of the present invention is to provide a fluid pulse-dampening apparatus having fluid degassing capabilities, wherein the apparatus is substantially configured to maintain laminar fluid flow therewithin.
By means of the present invention, an apparatus for simultaneously dampening fluid flow pulsations and degassing fluids passing through a semi-permeable tube is provided. This is achieved by forming the tube in a substantially elliptical-shaped configuration, with the tube being fabricated from a gas-permeable and liquid-impermeable material such as an amorphous perfluorinated copolymer. Through the use of such amorphous perfluorinated copolymers, tubes having sufficient flexibility to extend in a cross-sectional direction for fluid flow pulse-dampening characteristics may be fabricated without compromising fluid degassing characteristics. Through such an apparatus, design efficiency of liquid chromatography applications is enhanced by combining flow-dampening and degassing functionality into one apparatus, as described in the present application.
One embodiment of the flow-dampening degassing apparatus of the present invention includes a substantially elliptical-shaped flexible tube disposed in a chamber, which chamber is preferably operably coupled to a vacuum source such that the chamber has a reduced internal pressure. The tube is preferably sufficiently flexible to expand in a cross-sectional direction upon incursion of a fluid pulsation to thereby increase an inner volume and correspondingly reduce fluid pressure therein, while also being sufficiently resilient to return to its original configuration after the pulse has been dampened. The tube is operably coupled to a fluid pump, which pump may render fluid flow pulsations both upstream and downstream therefrom. The tube is preferably a gas-permeable and liquid-impermeable material, and is more preferably an amorphous perfluorinated copolymer such as TEFLON AF∞. The tube preferably has a wall thickness of between about 0.002 inches and about 0.010 inches, such that the tube can effectively dampen fluid pulsations of up to about 100 pounds per square inch. Such an embodiment of the flow-dampening degassing apparatus is preferably utilized in conjunction with a high performance liquid chromatography system.